Field of the Invention
The present invention relates to a conductive member, an image forming apparatus having the conductive member, a conductive particle contained in the conductive member, and a method for manufacturing the conductive particle.
Description of Related Art
In image forming apparatus using an electrophotographic process, generally, a toner image formed on a photoconductor is transferred from the photoconductor to an intermediate transfer belt, and then from the intermediate transfer belt to a recording medium. As the intermediate transfer belt, for example, electrically conductive, flexible endless belts have been used. Such a conductive belt is formed for example of a conductive composition such as resin or rubber in which conductive carbon black particles are dispersed. The conductivity of the conductive belt is adjusted by the amount of the conductive carbon black particles.
When the amount of the conductive carbon black particles exceeds a certain value, however, the electric resistance of the conductive belt decreases largely. Such a phenomenon wherein the electric resistance of a conductive belt decreases largely due to a slight increase in the amount of the conductive carbon black particles is called “percolation.” It is thus difficult to adjust the surface resistivity of a conductive belt to a level obtained when adding conductive carbon black particles in an amount near the amount where percolation occurs, e.g., 1.0×106 to 1.0×1013Ω/□, a level referred to as semiconductivity.
Known techniques for preventing percolation include covering the surface of conductive carbon black particles with silica (e.g., Japanese Patent Laid-Open No. 2002-270032), and physically covering the surface of conductive carbon black particles with resin (e.g., Japanese Patent Laid-Open No. 2012-46740). With these techniques, the formation of conductive paths due to contact among conductive carbon black particles is prevented.
In the former technique, covering of the surface of the conductive carbon black particles with silica is accomplished either by mechanical mixing of the conductive carbon black particles with silica or by contact of conductive carbon black particles with SiOx gas. With the method involving mechanical mixing, however, it is difficult to make uniform the thickness of the silica cover layer covering the surface of the conductive carbon black particles. With the method involving contact with SiOx gas, a silanol group exists on the surface of the silica cover layer and hydrogen bonding is formed between the covered conductive carbon black particles. Therefore, when the covered conductive carbon black particles are mixed in a matrix resin that constitute the conductive belt, the covered conductive carbon black particles aggregate easily and, in some cases, the dispersibility of the covered conductive carbon black particles becomes insufficient.
With the latter technique, the contact resistance between the conductive carbon black particle and the resin layer covering the conductive carbon black particle may become too high, or the thickness of the cover layer formed of resin may become uneven. It is therefore difficult to stably obtain a conductive member having desired conductivity.